(1) Field of the Invention
The present invention relates to a moving picture display apparatus that decodes and displays encoded moving picture data, and in particular to a light source control technique when displaying moving pictures on a liquid crystal display.
(2) Description of the Related Art
Liquid crystal displays (hereinafter referred to as LCDs), which are non-self-lighting, use a light source such as an external light or a backlight, and can be classified as transmissive, reflective, or projective according to the positional relationship between the light source and the liquid crystal panel.
Although higher screen luminosity is not necessarily better in an LCD, it can be said that basically text and images displayed on the screen can be seen more easily if the screen is brighter when the screen is viewed in a bright room or from a distance.
However, increasing the luminosity of the screen, in other words, the brightness of the light source, causes problems such as light leakage which causes black to appear less black on the actual screen, and increased heat emission by the light source.
In response to such problems, there are techniques that control the intensity of the light source in accordance with the brightness of the image to be displayed on the screen. This reduces the problem of black appearing less black, and also reduces the heat emission and power consumption by the light source (see Patent Document 1).
Referring to the block diagram in FIG. 13, a brief description is given of the image display apparatus disclosed in Patent Document 1. This image display apparatus receives an image in a YUV format that is a luma and chrominance format, converts the received image into an RGB image, and displays the RGB image.
A YUV-RGB conversion unit 31 converts a signal S31, which consists of a luma signal (Y) and chrominance signals (U and V) input in the YUV format as an image signal, into a primary color signal S34 in RGB format. In parallel with this conversion, a peak detection unit 32a detects a peak value S32 of the luma signal Y which shows the luma component of the input signal S31. The image display apparatus performs contrast correction with respect to the primary color signal S34 and the intensity of the light source 35 in accordance with this peak value, and displays a resultant image.
Adjusting the intensity of the light source and correcting the contrast in accordance with the peak value of the luminosity reduces the problem of black not appearing black in an image having low luminosity, and also heat emission and power consumption by the light source.    Patent Document 1: Japanese Unexamined Patent Application Publication No. H06-160811
However, it is not until after input of the image signal of the image to be displayed has ended that the peak value of the Y component is found. In other words, it is when input of the image signal of one display screen has finished that the peak value of the image signal of that display screen is found.
Consequently, when the peak value is found, the image signal of the display screen has already been converted into RGB and displayed. In other words, the peak value used to control the intensity of the light source and the like is the peak value found based on the previous display screen. This means that the peak value used in light source intensity control and contrast correction is not the peak value of the display screen being displayed.
This is problematic because in cases where, for example, the display screen changes from being a display screen having low luminosity to a display screen having high luminosity, the screen is not displayed appropriately because the control is not performed appropriately.
This problem can be solved by providing a memory that can be used as a buffer to store one display screen. However, since one display screen consists of a large amount of image data, problems of increases in circuit scale and cost arise if a large-capacity memory is added.